When should I ask for an official?

You may contact an official for help with (Code 41):

• Stalling
• Flagrant foot faults
• Extreme grunting
• A medical or bleeding time-out
• A scoring dispute
• A pattern of bad calls

You may refuse to play until an official responds.

Stalling includes warming up longer than allowed, playing at about a third of your normal pace, taking more than 90 seconds at a changeover or 2 minutes at a set break, starting an argument to rest, and excessive ball bouncing before serving (Code 40).

Otherwise, you need an official's permission to leave the playing area (USTA Reg. IV.C.5). You're not entitled to have an official removed from your match (Reg. IV.C.8).